[Secretion of insulin. Hypotheses at present under discussion (author's transl)]

Proinsulin is dissociated into insulin and C-peptide in the Golgi zone and in the beta-granules which fulfil a storage and transport function at the same time. Through an active transport process involving the microtubular and microfilament cytoplasmic system, the granules arrive at the cell wall and there they are emiocytotically excreted. At a still completely unknown spot on this secretory route, control of the secretion rate by calcium ions and cAMP-dependent phosphorylation seems possible. Calcium and cAMP as signal transmitters are again subject to the positive and negative modulating receptor-transmitted effect of adrenergic and cholinergic transmitter substances and beta-cytotropic peptide hormones. The basis of every modulation of the secretory function, however, is a secretion signal dependent on the concentration of glucose itself and glucose metabolites (only one?) on the one hand, and on the other on the energy resulting from endoxidation of glucose in the form of high energy phosphates.